Sensor

Abstract

A sensor includes: a complex transfer function calculator calculating complex transfer functions; a living body component extractor extracting living body information; a correlation matrix calculator calculating a target correlation matrix from the living body information; a noise information storage recording a noise correlation matrix; a first headcount information calculator calculating first headcount information that is a tentative number of persons present in the predetermined space, based on the target correlation matrix and a threshold calculated from the noise correlation matrix; a MUSIC spectrum calculator estimating position candidates for the living bodies, using the target correlation matrix, and outputting likelihood spectra indicating likelihoods of the respective living bodies being present in corresponding positions; and a second headcount information calculator estimating second headcount information that is a more accurate number of living bodies or positions from position information that is based on the likelihood spectra and can include the position candidates.

The invention claimed is: 
     
       1. A sensor that estimates a total number of living bodies, the sensor comprising:
 a complex transfer function calculator that calculates complex transfer functions from reception signals that are signals transmitted in a predetermined space from a transmission device including N transmission antenna elements, where N is a natural number greater than or equal to 2, and received during a predetermined period by M reception antenna elements, where M is a natural number greater than or equal to 2; 
 a variation component extractor that extracts living body information that is a variation component in the predetermined space; 
 a correlation matrix calculator that calculates a target correlation matrix from the living body information extracted by the variation component extractor; 
 a noise information storage that records a noise correlation matrix measured in the predetermined space; 
 a first headcount information calculator that calculates a threshold from the noise correlation matrix and calculates first headcount information by using, as a tentative value of the total number of living bodies that are present in the predetermined space, a total number of eigenvalues being greater than or equal to the threshold in the target correlation matrix; 
 a likelihood spectrum calculator that estimates a plurality of candidates for positions of the living bodies by a predetermined position estimation method, using the first headcount information and the target correlation matrix, and outputs likelihood spectra indicating likelihoods of the respective living bodies present in corresponding ones of the positions; and 
 a second headcount information calculator that estimates, by a predetermined method, second headcount information or positions from position information that is based on the likelihood spectra and can include the plurality of candidates for the positions, the second headcount information being a more accurate number of living bodies. 
 
     
     
       2. The sensor according to  claim 1 , wherein
 the first headcount information calculator calculates the first headcount information based on eigenvalues of the target correlation matrix and eigenvalues of the noise correlation matrix. 
 
     
     
       3. The sensor according to  claim 2 , wherein
 the first headcount information calculator outputs, as the first headcount information, a total number of eigenvalues that are greater than the threshold, the eigenvalues being obtained by decomposing the target correlation matrix. 
 
     
     
       4. The sensor according to  claim 1 , wherein
 the noise correlation matrix is a correlation matrix measured from the reception signals that are measured under a condition that corresponds to a state where no person is present in the predetermined space. 
 
     
     
       5. The sensor according to  claim 1 , wherein
 the first headcount information calculator uses, as the threshold, a maximum one of or a total sum of eigenvalues in the noise correlation matrix. 
 
     
     
       6. The sensor according to  claim 1 , wherein
 the threshold used by the first headcount information calculator is a value obtained by increasing or decreasing a maximum one of or a total sum of eigenvalues in the noise correlation matrix at a predetermined ratio. 
 
     
     
       7. The sensor according to  claim 1 , wherein
 the threshold used by the first headcount information calculator is a value obtained by adding or subtracting a predetermined value to or from a maximum one of or a total sum of eigenvalues in the noise correlation matrix.